This invention relates to a thin film magnetic element that is applied to wireless signal transmission, a new functional element for communication, and the like.
In recent years, in contrast with the field of electronics, in which electron charges are applied, attention has been given to the field of spintronics, in which electron charge and a spin are simultaneously used (Non-Patent Reference 1). Due to rapid development of magnetoresistive effect elements, which are represented by a giant magnetoresistive (GMR) effect and a tunneling magnetoresistance (TMR) effect, spintronics significantly contributes to industry in the form of hard disk drives (HDD) and magnetoresistive random-access memories (MRAM).
In a magnetoresistive effect element, it is known that as a spin is transmitted and transported, it becomes energy (spin-transfer torque) that rotates a spin of another ferromagnet. If this spin-transfer torque is used, at a certain constant energy, spin oscillation and resonance phenomena occur. Industrial uses have been proposed, as devices such as high-frequency oscillators, detectors, mixers, and filters that use these phenomena (Patent Reference 1). It is known for a high frequency characteristic of a magnetoresistive effect element to be controlled by an applied magnetic field and a spin-transfer torque (Non-Patent Reference 2).
The following application can be considered for an element using a high frequency characteristic of a magnetoresistive element (hereafter referred to as a “thin film magnetic element”). For example, a low-loss variable matching circuit must be implemented that can be used at high frequency areas of 1 GHz or higher for multi-banding and active tuning that are being considered for increasing the functions of a portable terminal. However, if a varicap diode is used for the matching circuit, a Q value is caused to be deteriorated, and an operation voltage is caused to increase, at high frequency areas of 1 GHz or higher. In contrast, these inventors discovered that if a thin film magnetic element is used for the matching circuit, there is a possibility that it will surpass a varicap diode in view of the Q value and the operation voltage, and these inventors have been working on the development. As mentioned earlier, a high frequency characteristic of a thin film magnetic element can be controlled by an applied magnetic field, but when industrial uses are considered, an element structure is needed that includes a magnetic field application mechanism that can variably, and over a wide range, control an applied magnetic field.
As an example of an element structure including a magnetic field application mechanism that variably controls an applied magnetic field, a structure is proposed in which a composite magnetic field of (i) a coil magnetic field by current control and (ii) a bias magnetic field by a bias hard magnetic layer is applied to a magnetoresistive effect film (Patent Reference 2).
Furthermore, a structure is proposed in which, by detailed control of a shape of a pair of soft magnetic layers, which is formed so as to sandwich a magnetoresistive effect film, a magnetic field applied to a magnetoresistive effect film is strengthened (Patent Reference 3).